The present invention concerns mechanically controlled drum brakes, this mechanical control being able to constitute the principal actuating means of this drum brake, or an auxiliary actuating means in the case of a drum brake already possessing a principal brake motor. In the latter case, the mechanical control may constitute a parking brake, also known as a handbrake or an emergency brake.
In a known manner, drum brakes are constituted by two shoes each presenting a web and a rim whose face facing the drum receives a friction lining, the drum brake being arranged on a support plate fixed to the stub axle of the wheel with which it is associated, the drum being firmly attached to the wheel to be braked.
Generally, a mechanical control lever is provided, articulated at one of its ends on the web of one of the shoes and possessing, at an intermediate point, near to this articulation, a notch provided to cooperate with a strut allowing the shoes to be stressed apart under the action of a control cable hooked to the other end of the lever.
Such drum brakes are well known to a person skilled in the art. U.S. Pat. No. 4,595,084 describes, for example, a mechanical control lever for such a brake. However, according to the teaching of this document, the control cable of the lever has to be mounted on the brake during the final phase of assembly of the latter while it is not yet covered by the drum. It is then usual to make one or more loops with the cable to prevent the latter, in its free state, being an inconvenience during fitting of the brake to the chassis of the vehicle. However, such loops remain a handicap for the manufacturer, and it is desirable that the installation of the cable can be deferred until all the parts of the chassis of the vehicle are assembled, including the brake with its drum, and that the cable may only thereafter be connected to the brake.
It has thus been proposed, for example by the documents GB-A-1,314,230 or U.S. Pat. No. 2,945,564, to articulate the actuating lever on the strut itself, the lever, on which the control cable is fitted, passing through an opening in the support plate. In this way, the control cable may be fixed to the brake after the latter has been fitted to the chassis of the vehicle.
Such devices however possess numerous disadvantages: the actuating lever being articulated on the strut, which is essentially a moving part, it is necessary to find a bearing point for the operation of the lever. According to the aforementioned documents, the fixed bearing point is provided by the reference surface constituted by the internal face of the support plate, on which the strut comes to rest. It then follows that the actuation of the lever causes high friction of the strut on the support plate, so increasing the force to be overcome to separate the shoes from each other, causing wear of the strut and of the support plate, and inducing extra stresses within the support plate.
In addition, these devices do not allow freeing of the brake to ease the installation of the brake drum, and they do not lend themselves well to automated installation of the control cable. Another disadvantage of these devices lies in the fact that, due to the absence of the automatic adjustment, the travel of the control cable increases with the wear of the friction linings.